Sanctuary City Laws: What They Do And Don't Support06:06

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San Francisco is one of hundreds of so-called 'sanctuary cities' around the country (diversey/Flickr)

When 32-year-old Kathryn Steinle was shot to death on a pier in San Francisco last week, attention immediately turned to her accused killer. That's because the 45-year-old immigrant had a long felony rap sheet and a history of deportations.

It has also been reported that U.S. Immigration and Customs Enforcement (ICE) had turned over the suspect, Francisco Lopez-Sanchez, to city authorities on March 26 on an outstanding drug warrant and asked the city to notify them when he got out - something San Francisco officials apparently did not do.

That's because San Francisco is one of hundreds of so-called "sanctuary cities" around the country. And while critics, including Republican presidential candidate Donald Trump, say this murder highlights the problem with sanctuary cities, supporters say the case is an outlier and that local officials should have turned Lopez-Sanchez over to authorities, even under the existing sanctuary city laws.